Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$108.55	12.208%	$121.8018	$121.80	$121.80	$121.80
Purchase #2	$50.49	13.326%	$57.2183	$57.22	$57.20	$57.20
Purchase #3	$104.55	11.247%	$116.3087	$116.31	$116.30	$116.30
Purchase #4	$246.52	10.175%	$271.6034	$271.60	$271.60	$271.60
Purchase #5	$129.60	7.410%	$139.2034	$139.20	$139.20	$139.20
Purchase #6	$204.86	7.812%	$220.8637	$220.86	$220.85	$220.90
Purchase #7	$83.84	6.534%	$89.3181	$89.32	$89.30	$89.30
7 purchase totals =	$928.41		$1,016.3174	$1,016.31	$1,016.25	$1,016.30